I need to join two short iPhone videos into one, flip them upside down (because many players ignore iPhone's orientation flag), and insert a 5-second black screen that will say "20 minutes later..." between the two segments.

Is it possible to do all these steps without re-encoding? If no, is it possible to do ANY of them without reencoding (especially changing the vertical orientation flag without reencoding would be very nice).

Shoot your intertitle with your phone.
Open all of the files in Quicktime Pro.
Rotate your wrongly oriented file as save as a self contained quicktime movie.
Set your in-point to the end of movie 1
set in and out points at the beginning and end of movie 2 and paste them to the end of movie 1
Set the end of the newly elongated movie 1 as your new inpont
set in and out points at the beginning and end of movie 3 and paste them to the end of movie 1.
Save as a new self-contained movie.

OK. I opened the original file in QT Pro, and the orientation flag seems to be correct. But when I remuxed it to MKV to change the audio track, it came out flipped, so I assumed it was the original file's fault. Could it be something within mkvtoolnix instead?

Follow-up question. I made a 1920x1080 black PNG image in Photoshop and added it between the two clips in Quicktime. How do I change the duration of the black screen? For example, I'd like it to be 5 seconds. If the video is 30fps, I hope it doesn't mean I have to paste that image 150 times?

By the way, what's the term video professionals use for a black screen with a message in between clips?

Follow-up question. I made a 1920x1080 black PNG image in Photoshop and added it between the two clips in Quicktime. How do I change the duration of the black screen? For example, I'd like it to be 5 seconds. If the video is 30fps, I hope it doesn't mean I have to paste that image 150 times?

By the way, what's the term video professionals use for a black screen with a message in between clips?

Looks like QuickTime Pro cannot export a graphic as a video file, so I'll go back to my original suggestion of shooting it with the phone as the simplest way to do it.

Shooting what with the phone? The title? I don't see that in your previous post.

First line in my original post. Make it in photoshop or some graphics program. Print it out or shoot it off the screen with the phone. This is the simplest way to do it while matching the parameters of the other files. Other methods get way more complicated and harder to merge. (The second word in your topic is "simple.")

Hmm, I think it will cost half the printer's toner to print a pure black screen, plus I really suck at shooting videos and it's likely to come out shaky, and the white letters won't look very white in a dark closet.

So I guess I need to find a program for Windows that can make this 5-second "intertitle." I really didn't plan on taking Filmmaking 101 for something so simple, but that's always how this works.

Well, they do produce valid (and I assume standard-compliant) streams, so if I need to muck with remuxing/demuxing them, so be it.

The only thing I"m not willing to do is re-encode to avoid quality loss. So I guess the issue now is how to produce the 5-second intertitle that QT PRo will accept for the purposes of joining them with the other videos.

Well, they do produce valid (and I assume standard-compliant) streams, so if I need to muck with remuxing/demuxing them, so be it.

Part of how they achieve their efficiency is by using variable frame rate video, it can go from 20 - 30 fps It's a semi-brilliant solutiion to variable lighting conditions in the context of standalone videos that are meant to be instantly uploaded and shared. Once you start editing these things together it can get pretty messy. Quicktime Pro hides the inconsistencies on playback.

If you go to a standard NLE like Vegas Movie Studio (or even a fancy one like Vegas Pro or Premiere or Avid) you can easily end up with some blended images in some shots and perfectly clear images in others. All of it requires reencoding, but of course you have much more control over the finished product. Many folks who shoot iphone for editing use apps which force the framerate and allow manual exposure and focus.